In recent years, an interest has been directed to the relationship between an increase in the level of cholesterol in the serum and a human health condition. It has been pointed out that the level of cholesterol in the serum is associated with the amount of cholesterol deposited in the blood vessel system and the deposition of cholesterol in the blood vessel system brings about e.g. lesion of coronary artery, which is responsible for ischemic heart disease.
Drugs for reducing the level of cholesterol in the serum have been developed. These drugs, however, were effective in controlling blood cholesterol to an appropriate level, but ineffective in inhibiting absorption of cholesterol from the digestive tracts and deposition of cholesterol on the wall of blood vessels.
ACAT is an enzyme that catalyzes the synthesis of cholesteryl esters from acyl coenzyme A and cholesterol and plays an important role in metabolism of cholesterol and its absorption from the digestive tracts. It is believed that ACAT occurs in the site of mucosa cells of the intestinal tracts and is active in esterification and incorporation of cholesterol derived from the diet. On the other hand, the cholesterol deposited on the wall of blood vessels is the esterified cholesterol. The cholesterol accumulated in the foam cells which plays in important role in the formation of atherosclerosis lesion is also esterified cholesterol. The enzyme that catalyzes the esterification of cholesterol in these sites is also ACAT.
Accordingly, the inhibition of an ACAT activity can result in inhibiting the incorporation in vivo of cholesterol derived from the diet and further the formation of cholesteryl ester in specified cell sites.
Compounds having an ACAT inhibitory activity are disclosed in EP 0450660 A1 and EP 0477778 A2. However, those known compounds have only an ACAT inhibitory activity and give no effect on the oxidative modification of LDL causing the foam cell transformation of macrophage which is an important phenomenon for the formation of atherosclerosis lesion.
The foam cells which play an important role in the formation of atherosclerosis lesion are a product of uptake of oxidatively modified LDL into macrophage which results in the foam cell transformation of the macrophage. It is reported by Diane W. Morel et al. (Atheroma, Vol. 4, pages 357-364, 1984) that, the oxidatively modified LDL causes foam cell transformation of macrophage and plays an important role in the formation of atherosclerosis lesion. A report of TORU KITA et al. (Proc. Natl. Acad. Sci. U.S.A., Vol. 84, pages 5928-5931, 1987) demonstrates that prevention of the oxidative modification of LDL induces regression of the atherosclerosis lesion. Therefore, inhibition of the oxidative modification of LDL, in addition to the abovementioned ACAT inhibitory activity, is very important in preventing the formation and progression as well as inducing regression of atherosclerosis lesion.
Under such circumstances, it has been desired to develop the compound having an ACAT inhibitory activity and being capable of inhibiting an oxidative modification of LDL or the like, since such compound may decrease the serum cholesterol level and inhibit the oxidative modification of LDL cholesterol deposited on the blood vessel or tissue, thus being effective for inhibiting the formation and progression of atherosclerosis lesions and inducing its regression.